A 4.2 kg block and a 2.8 kg block with a compressed spring between them are held together by a string. The spring has a spring constant of 120 N/m and is compressed by a distance of 0.1 m. The blocks are sitting at rest on a frictionless surface, then the string breaks.
a) Use conservation of momentum to determine a relationship between the new velocities of the two blocks.
b) Use conservation of energy to determine the new velocities of the two blocks, and their kinetic energies.